A dramatic new glass office tower is being planned for Park Avenue, The Post has learned.

The 50-story skyscraper, designed by Skidmore Ownings Merrill, would be built by Max Capital on and around the current 21-story 237 Park Ave.

Skidmore most recently designed the AOL Time Warner Center and the Farley Post Office Penn Station project, and did a renovation for Max Capital at 360 Madison Ave.

The Park Avenue development is feasible because Max Capital owns the neighboring Helmsley Building, and the site is zoned so larger buildings can be constructed with city permission.

“They already own a million square feet of air rights,” said one real estate source.

At the end of 1999, Max Capital purchased the 1.1 million square footer, also known as Park Avenue Atrium, for $372 million.

At the time, they figured out there was money to be made out of thin air.

The company, chaired by N. Richard Kalikow, boasts Robert M. Bass as a quiet investor. They already owned the Helmsley Building, the landmark office giant to its west and it was the ownership of both buildings that provided the key for the new plans.

They had purchased the 1.52 million-square-foot Helmsley Building from Leona Helmsley in August 1998 for $253 million, and it will now contribute some air rights.

Between the two properties, however, sits a long demapped street that will also add to the total.

The white 237 Park Ave. was developed by Olympia & York and designed by Edward Durell Stone & Associates – the architect of the controversial 2 Columbus Circle/Huntington Hartford Museum that will soon be sold by New York City for redevelopment.

Other sources said Max Capital is working with lawyer Bob Davis of Robinson, Silverman to prepare a proposal for City Planning. Davis did not return calls for comment. That filing would start the Uniform Land Use review process, which is necessary to get the approvals to build the tower.

The company quietly included a rendering of the project in its brochure last year. Max Capital President Adam Hochfelder has also made it known to brokers that they would build it when a tenant came. The company declined comment.